In this study, we aim to compare the criteria for sensitizers among national organizations in various countries and international organizations, and to specify whether each Pollutant Release and Transfer Register (PRTR)-designated chemical substance is a sensitizer by each organization. The definition of sensitizing chemicals and the designation of respective sensitizers according to the PRTR law, Japan Society for Occupational Health (JSOH), American Conference of Governmental Industrial Hygienists (ACGIH), European Union (EU), and Deutsche Forschungsgemeinshaft (DFG) were studied. Of the 435 PRTR-designated chemical substances, 15 are listed as sensitizers according to the PRTR law, 16 as sensitizers of the airway and 21 as sensitizers of the skin by JSOH, 12 as sensitizers (no discrimination) by ACGIH, 19 (airway) and 85 (skin) by EU, and 15 (airway) and 43 (skin) by DFG. Only 9 substances were designated as sensitizers by all these organizations. The variation in the designation of sensitizers is accounted for by the differences in the classification criteria and grouping of chemical substances. JSOH limits the definition of sensitizers to substances that induce allergic reactions in humans and uses only human data. Other organizations utilize not only human evidence but also appropriate animal tests. In addition, EU designates an isocyanate as a sensitizer except those for which there is evidence showing that they do not cause respiratory sensitivity. The worldwide enforcement of the globally harmonized system (GHS) of classification and labeling of chemicals could promote not only the consistent designation of sensitizers among national and international organizations, but also the development of testing guidelines and classification criteria for mixtures.